1. Field of the Invention
The present invention generally concerns water purification systems.
The present invention particularly concerns the purification of water in swimming pools, spas, hot tubs, water storage tanks, wells and water cooling towers by use of galvanic cells in order to inhibit the growth of bacteria, fungus and algae while significantly reducing the amount of chemicals (chlorine, bromine, hypochlorite, persulfate, ozone, etc.) necessary to maintain water quality.
2. Description of the Previous Art
2.1. Water Purification
The paramount function of water treatment is to destroy harmful microorganisms. This is usually accomplished by adding oxidizing agents such as chlorine, iodine and oxygen. In swimming pools and spas, the treatment of water to eliminate microorganism contamination ordinarily incorporates chemical treatment in combination with a mechanical filtering usually accomplished by drawing water from the pool with a pump, forcing it through a filter and returning it to the pool. Because the mere addition of a quantity of a chemical in liquid or soluble form permits the circulation system to effectuate quick dispersal, sanitization treatment is an easy task. Chlorine is typically used as a sanitation agent. However, chlorine is malodorous, rather inefficient, unhealthful, and not particularly economical.
At ordinary temperatures, chlorine is a gas, difficult to handle, and is not generally available. Accordingly, chlorine used in pools and ponds is combined with some compound that dissociates upon addition to pool water. Chlorine is popularly introduced as a constituent of calcium hypochlorite, sodium hypochlorite, chlorinated isocyanurates, or some other acid, or as a salt. If added as a salt, additional chemicals are required to avoid harmful accumulations of any other constituents of the salt, resulting in the problematic requirement of maintaining a chemical balance.
The process of purification of pool water using electrolysis has already been developed, and is well known in the art. Shindell, in U.S. Pat. No. 4,328,084 (1982) describes a water purification system employing salt in quantities sufficient to make the water slightly conductive and circulating that water through the electric field between a pair of dissimilar metal plates in order to dissociate salt ions from the water. The dissociated ions of salt and water are converted to oxidizing agents capable of destroying organic matter, which is converted to substances that can be removed by mechanical filtration. The process reportedly results in economical and effective purification. However, a major problem arises when a purification cell is placed in the circulation piping. The pump must operate continuously to maintain an effective level of chlorine or oligodynamic ions. This is not a problem in large commercial pools, however, in residential pools, the cost of continued operation becomes prohibitive. Also, governmental restrictions apply and costs of installation are high.
Metallic ions are known to kill or control algae and bacteria. It is well established that silver and copper ions are effective bactericides and algaecides. Treatment with silver has been used by NASA to purify water on the Apollo space missions. The practice of using silver and copper vessels to improve water quality dates back to ancient times. Ancient Phoenicians stored wine in silver urns to preserve it, providing one the earliest recorded examples of use of this metal for that purpose. Zinc, aluminum, and gold ions are just a few additional metals that can be used similarly.
Dahlegren, U.S. Pat. No. 4337136, (1982), purifies pool water by using a pair of silver-copper alloy electrodes extending from a floating container. Electrical energy is provided by a battery, using a timer switch that reverses the current as required to reduce erosion of the electrodes. The operating life of such a cell is limited by the requirement of batteries.
Sherman, in U.S. Pat. No. 5,085,753, describes a water purifier with a buoyant housing for supporting a purification cell below the water's surface and for supporting a solar cell array for providing power for the purification cell. The cell operation includes electrolytic processes, electrocution and oxidation to destroy bacteria and algae.
There are two types of undesirable elements in pool water: 1) impurities in suspension, in the form of precipitates or colloids, and 2) dissolved, extremely small, electrically charged impurities in the ionic state. To eliminate these impurities, flocculation processes--consisting of introducing a reactant into the water to create colloids with adsorption properties--have been used. The colloids cause flocculation, which encloses the impurities in suspension. Large particles are formed and are separated from the water by filtering. To facilitate flocculation, the pH of the water has to be adjusted, in many cases, to below 7.4 or above 8.5.
2.2. Water Purification With Metal Ions
Conventional purification devices use either (i) an excess of anodic reaction products, (ii) a particular linear relationship between purification cell current and treated water temperature, (iii) addition of sodium persulfate to water in which copper and silver ions have been added from copper-silver electrodes immersed in the water, or (iv) addition of salt in sufficient quantities to make the water slightly conductive followed by circulating the slightly conductive water through an electric field between a pair of electrode plates. These conventional devices and methods have generally been uneconomical and inefficient, and have focused on producing and regulating a DC current from an AC power source so as to maintain the safety of swimmers. The equipment is expensive, complicated and generally requires special installation and monitoring, thereby increasing manufacturing, operating and liability insurance costs.
Solar powered purification cells can overcome some of these problems, However, other drawbacks such as excessive gassing, corrosion, and accumulation of scale and deposits at the purification cell electrodes, result in reduced efficiency, destruction of the cell and/or the necessity of repetitively cleaning the electrodes.
In U.S. Pat. 5,279,748, issued to Hackett, water is passed through an "electrolytic filter" consisting of packed granules of copper and zinc, or "a copper-zinc filter media." "As water passes through the electrolytic granules, a chemical reaction causes metal hydroxides to form in controlled amounts. These controlled releases of oxides are carried into the filtered water where they kill bacteria and provide a hostile environment for algae and fungus growth." The amount of ionized metal entering the pool is controlled by varying the flow rate of water entering the electrolytic filter independent of the physical straining filter. The electrolytic filter is impervious to the bacterial growth to which similar filters (composed of other materials) can be susceptible. Hackett's device is claimed to eliminate the need for chlorine.
U.S. Pat. No. 4,492,618 to Eder discloses a method in which electrodes of a copper-silver alloy are dissolved in the treated water via the application of a periodically reversed direct current. The electrically induced dissolution of the electrodes liberates copper and silver ions into the water. Sodium persulfate is added to the water for the "oxidation of organic matter."
In U.S. Pat. No. 4,608,247 issued to Heinig, silver is deposited on a large surface area support and combined with carbon to produce a composition favorable to the dissolution of silver ions in water.
In U.S. Pat. No. 5,352,369, also issued to Heinig, a method is described in which silver deposited on a large surface area alumina matrix acts as a catalyst "in the presence of oxygen to form an active oxidizer in the water." This active oxidizer is claimed to be effective in the containment of bacterial and algal growth.
LeMire, in U.S. Pat. No. 4,935,116, describes a device consisting of concentric cylinders of dissimilar metals (copper and silver) that are electrically connected, with provisions to pass water to be treated in the annulus of said cylinders. The dissimilar metals form a voltaic cell whereby the metals are eroded to supply copper and silver ions to the water.
2.3. Silver Water Purification
Silver-based water purification systems offer the most reliable and cost-effective alternatives to chlorine, a chemical that is increasingly coming under fire for the carcinogenic byproducts it leaves in water. Because of increasing pollution, utilities are forced to put far more chlorine into the supply chain. Recently, chlorine has been shown to produce by-products linked to cancer in laboratory animals, prompting an immediate US government review. These same byproducts have been generated by chlorination for a long time, but never in the quantities that are now being seen.
In Britain, silver ionization is being developed for mainstream water systems. Capitalizing on silver's long-known biocidal properties and safety factors, the Institute of Water Ionization Technologies, UK, has developed silver ion generators for municipal water supplies. A recent project to study the control of Legionnaires disease by using silver ions was funded by the UK Department of the Environment. The disease is named after Legionella pneurnophilia, an organism that is widespread in small quantities within natural water sources. The bacteria is lethal at a water temperature of 95.degree. F., but can be killed at temperatures between 135 and 140.degree. F. Of the methods tested, silver/copper ions in soft water were found to be most effective. The copper ion disrupted the enzyme structures of the cell, allowing the silver ion to penetrate inside, where it rapidly inhibited the cell's life support system.
U.S. regulations allow a silver level of 100 ppb in drinking water, but a silver level of only 20 ppb kills Legionella. A proposed European Union Drinking Water Standard has removed any upper limit for silver in drinking water, following the World Health Organization's Guidelines for Drinking Wafer Quality, which determined that it is unnecessary to recommend any health-based guidelines for silver, as it is not hazardous to human health. Silver ion generators are currently being used in intensive care and heart transplant units of hospitals, and for poultry processing, engineering, brewing, cooling towers and swimming pools.
According to the most recent research on the swimming pool industry, published in 1993 by the National Spa and Pool Institute, 6.6 million individuals in the United States own pools, 3.4 million of which are in-ground and 3.2 million are aboveground. NSPI estimates that approximately 160,000 in-ground pools are built annually in the United States, in addition to about 475,000 aboveground pools. Silver-based mechanisms for keeping swimming pools sanitized are gaining widespread popularity among pool owners preoccupied with the mounting health hazards of chlorine.
Silver-copper ion systems have sanitized tens of thousands of swimming pools worldwide for several decades, inactivating organisms including Bacillus typhosus, Legionella pneumophila and E. coli. Copper ions in the system have eliminated unwanted algae growth in pools, and have supplemented silver in controlling other pathogens, such as the polio virus. The technology works by producing positively charged ions that attack and destroy the negatively charged cells of organisms like bacteria and algae. The positively charged ions also work by interfering with the metabolism of organisms like bacteria and algae.
The purification method named the number one alternative to chlorine, based on research conducted by Swimming Pool and Spa Age magazine, is a silver catalyst system that has the capacity to instantly destroy bacteria and viruses. The system deposits silver microcrystals on the inside of a flow-through cartridge, which feeds oxygen into the water flow. The oxidized silver destroys bacteria, viruses and organic matter. Tests performed by the U.S. Environmental Protection Agency (EPA) at the University of Arizona, for example, found that the cartridge reduced the presence of E. coli in water by 99.96 percent within five seconds.
The use of silver in swimming pool sanitation is growing because of the many other advantages these systems offer. Silver systems are less expensive operationally than chlorine and other chemical systems. Also, silver does not evaporate from the water leaving the pool unprotected and does not stain the skin or bleach clothing.
2.4 Galvanic Cells
It is known, by practitioners in the art, that each metal has its own electrochemical potential. Additionally, it is known that when two dissimilar metals, each with different electrochemical potentials are immersed in a conductive solution and electrically connected together, a galvanic cell or battery will be formed; such that current will flow from the metal of lower electrochemical (anode) potential to the metal of high chemical potential (cathode). Moreover, it is known that the metal of lower electrochemical potential will be dissolved into the electrolyte at a rate proportional to the current flowing between the two electrodes. This process transpires when a strip of a metal such as silver is immersed in water containing ionic species. A strip of another metal, such as platinum, is immersed in the water and is electrically connected to the silver strip, commonly by wire via an ampere meter. Current flows from the silver strip through the wire and ampere meter to the platinum strip due to the potential difference between the two metals. At the surface of the silver strip metallic silver atoms lose electrons to form silver ions. The electrons liberated by the oxidation of metallic silver flow through the electrical connection between the two metals, comprising a current which can be detected by the ampere meter. At the surface of the platinum, electrons typically react with oxidizing species, such as hypochlorite ions.
A galvanic cell is a simple and effective means of introducing small quantities of beneficial metal ions into water. What has been misunderstood by previous investigators (LeMire and Hackett) is that the metal of higher electrochemical potential is cathodically protected by the flow of current in the galvanic cell and is therefore inhibited from dissolving. In fact, this effect is exploited in galvanized steel and in other applications such as the use of a sacrificial zinc electrode for underground tank and marine applications. Therefore, the devices described by LeMire and Hackett will only be effective in dissolving the metal of lower chemical potential. Silver, which has a relatively high electrochemical potential, will not be appreciably dissolved.